The present invention relates to a method of printing thick film patterns on a glass or plastic substrate.
Currently, patterns on substrates such as automotive windshields and back lights are formed, primarily, by screen printing processes. The limitations of the screen printing process such as variable uniformity in line thickness, inability to print lines thinner than 0.025 mm, and narrower than 0.25 mm with currently available screen fabric, are well known. Screen printing is also an expensive process, not only in terms of the manufacture of the silk screens themselves, but also the complicated nature of the process of changing from one screen to another in the printing process.
Accordingly, it would be desirable to have available a method of printing very precise patterns on glass or plastic substrates which is cost effective and gives consistent results. Additionally, it would be desirable if such a system would be capable of changing printing inks and patterns relatively simply and in a short period of time.
Those skilled in the art of printing on glass and polycarbonate substrates have continued in their attempts to develop systems which can produce very precise patterns in a repeatable and cost effective fashion on large glass and polycarbonate substrates such as automotive windshields and back lights.
U.S. Pat. No. 4,692,351 describes a drawing apparatus comprising a drawing nozzle having a discharge hole for a paste, X-Y drive means for moving the drawing nozzle, and a substrate for drawing a thick film circuit on the substrate, up and down drive means for relatively moving the drawing nozzle and the substrate in directions perpendicular to the substrate, and control means for controlling the discharge rate of paste from the discharge hole and for controlling the X-Y drive means, as well as, the up and down drive means. The discharge amount of the paste from the discharge nozzle is controlled in accordance with the relative moving speed between the drawing nozzle and substrate. Furthermore, a drawing apparatus is also arranged to detect the relative speed of movement between the drawing nozzle and substrate and to control the discharge rate of paste from the discharge hole in accordance with the detected relative speed of movement. The up and down drive or nozzle lifter comprising a magnet is attached to the upper supporting plate.
U.S. Pat. No. 4,664,945 describes a method of forming thick film circuits comprising laterally moving a writing head containing a paste for forming a thick film circuit relative to a board on which the circuit is to be formed. The writing head is maintained in close proximity to the board, extruding the paste from an extrusion means connected to the writing head by supplying pressure from a source of compressed air to the extrusion means, thereby, depositing the paste on a top surface of the board.
U.S. Pat. No. 4,661,368 describes a method of depositing a dose of flowable material from a tip onto a surface comprising the steps of advancing the tip toward and into engagement with a portion of a surface in sensing a reactive force on the tip from the surface, recording a position on a path of advancing the tip when a particular value of the sensed reactive force is attained. Halting the advancement of the tip when a desired position has been attained and retracting the tip away from the surface and depositing a dose of flowable material onto the desired portion of the surface.
U.S. Pat. No. 5,091,003 discloses a method of printing on glass utilizing a non-contact ink jet printer and a specialized ink composition comprising a mixture of silver nitrate and a carrier of said ink having a low viscosity compared to those normally utilized in a non-contact ink jet printer.
The present invention relates to the use of an orifice printing system, wherein inks are dispensed through a writing orifice, to print thick film patterns on a glass or plastic substrate.
The invention is particularly directed to the use of an orifice printing system for printing a pattern on an automotive glazing such as a windshield or back light. More particularly, it is directed to printing very precise patterns on glass or polycarbonate substrates, which patterns may be formed from electrically conductive materials, thus enabling such patterns to conduct electrical current. Such patterns may then serve as devices for defogging or defrosting the glazing, and also as antennas for various purposes, such as radio, telephone, and the like.
An orifice writing system such as that disclosed in U.S. Pat. No. 4,485,387, which is hereby incorporated by reference, is particularly well-suited for use in the present invention, as it can produce lines of very precise and uniform width, uniform cross sectional area, and clean start and termination of such lines. These characteristics can be maintained at a variety of printing speeds over large areas and with greater repeatability than with screen printing methods currently in use. The appearance of the patterns thus produced is enhanced. If electrically conductive printing materials are used, the performance for conducting electrical current in terms of milli-ohms/square is substantially enhanced. A further advantage of such an orifice writing system is that the source of the printing ink can be changed in a matter of minutes and a pattern to be written by the system can be changed via microprocessor in minutes, as well.
Heretofore, such orifice printing systems have been used primarily for printing very precisely but on a small scale, such as for electronic circuit boards and the like. The inks utilized in such systems have been relatively low viscosity inks. It is desirable in connection with the present invention, to utilize much more viscous inks than have been used in previous applications of orifice writing systems. The higher viscosity needed is on the order of 400% greater than has been used previously. Stated another way, the viscosity preferred for purposes of the subject invention is in the range of 50,000-190,000 pascal seconds.